Message-ID: <cd6f5d1f-bd89-5da2-96be-85c2311ca0a1@gmail.com>
Date:   Fri, 19 Oct 2018 15:25:40 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Eric Dumazet <edumazet@...gle.com>, andre@...t.net
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        netdev <netdev@...r.kernel.org>, rossi.f@...ind.it,
        Dimitris Michailidis <dmichail@...gle.com>
Subject: Re: Fw: [Bug 201423] New: eth0: hw csum failure



On 10/19/2018 02:58 PM, Eric Dumazet wrote:
> 
> 
> On 10/16/2018 06:00 AM, Eric Dumazet wrote:
>> On Mon, Oct 15, 2018 at 11:30 PM Andre Tomt <andre@...t.net> wrote:
>>>
>>> On 15.10.2018 17:41, Eric Dumazet wrote:
>>>> On Mon, Oct 15, 2018 at 8:15 AM Stephen Hemminger
>>>>> Something is changed between 4.17.12 and 4.18, after bisecting the problem I
>>>>> got the following first bad commit:
>>>>>
>>>>> commit 88078d98d1bb085d72af8437707279e203524fa5
>>>>> Author: Eric Dumazet <edumazet@...gle.com>
>>>>> Date:   Wed Apr 18 11:43:15 2018 -0700
>>>>>
>>>>>      net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends
>>>>>
>>>>>      After working on IP defragmentation lately, I found that some large
>>>>>      packets defeat CHECKSUM_COMPLETE optimization because of NIC adding
>>>>>      zero paddings on the last (small) fragment.
>>>>>
>>>>>      While removing the padding with pskb_trim_rcsum(), we set skb->ip_summed
>>>>>      to CHECKSUM_NONE, forcing a full csum validation, even if all prior
>>>>>      fragments had CHECKSUM_COMPLETE set.
>>>>>
>>>>>      We can instead compute the checksum of the part we are trimming,
>>>>>      usually smaller than the part we keep.
>>>>>
>>>>>      Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>>>>>      Signed-off-by: David S. Miller <davem@...emloft.net>
>>>>>
>>>>
>>>> Thanks for bisecting !
>>>>
>>>> This commit is known to expose some NIC/driver bugs.
>>>>
>>>> Look at commit 12b03558cef6d655d0d394f5e98a6fd07c1f6c0f
>>>> ("net: sungem: fix rx checksum support")  for one driver needing a fix.
>>>>
>>>> I assume SKY2_HW_NEW_LE is not set on your NIC ?
>>>>
>>>
>>> I've seen similar on several systems with mlx4 cards when using 4.18.x -
>>> that is hw csum failure followed by some backtrace.
>>>
>>> Only seems to happen on systems dealing with quite a bit of UDP.
>>>
>>
>> Strange, because mlx4 on IPv6+UDP should not use CHECKSUM_COMPLETE,
>> but CHECKSUM_UNNECESSARY
>>
>> I would be nice to track this a bit further, maybe by providing the
>> full packet content.
>>
>>> Example from 4.18.10:
>>>> [635607.740574] p0xe0: hw csum failure
>>>> [635607.740598] CPU: 4 PID: 0 Comm: swapper/4 Not tainted 4.18.0-1 #1
>>>> [635607.740599] Hardware name: Supermicro Super Server/X10SRL-F, BIOS 2.0b 05/02/2017
>>>> [635607.740599] Call Trace:
>>>> [635607.740602]  <IRQ>
>>>> [635607.740611]  dump_stack+0x5c/0x7b
>>>> [635607.740617]  __skb_gro_checksum_complete+0x9a/0xa0
>>>> [635607.740621]  udp6_gro_receive+0x211/0x290
>>>> [635607.740624]  ipv6_gro_receive+0x1a8/0x390
>>>> [635607.740627]  dev_gro_receive+0x33e/0x550
>>>> [635607.740628]  napi_gro_frags+0xa2/0x210
>>>> [635607.740635]  mlx4_en_process_rx_cq+0xa01/0xb40 [mlx4_en]
>>>> [635607.740648]  ? mlx4_cq_completion+0x23/0x70 [mlx4_core]
>>>> [635607.740654]  ? mlx4_eq_int+0x373/0xc80 [mlx4_core]
>>>> [635607.740657]  mlx4_en_poll_rx_cq+0x55/0xf0 [mlx4_en]
>>>> [635607.740658]  net_rx_action+0xe0/0x2e0
>>>> [635607.740662]  __do_softirq+0xd8/0x2e5
>>>> [635607.740666]  irq_exit+0xb4/0xc0
>>>> [635607.740667]  do_IRQ+0x85/0xd0
>>>> [635607.740670]  common_interrupt+0xf/0xf
>>>> [635607.740671]  </IRQ>
>>>> [635607.740675] RIP: 0010:cpuidle_enter_state+0xb4/0x2a0
>>>> [635607.740675] Code: 31 ff e8 df a6 ba ff 45 84 f6 74 17 9c 58 0f 1f 44 00 00 f6 c4 02 0f 85 d8 01 00 00 31 ff e8 13 81 bf ff fb 66 0f 1f 44 00 00 <4c> 29 fb 48 ba cf f7 53 e3 a5 9b c4 20 48 89 d8 48 c1 fb 3f 48 f7
>>>> [635607.740701] RSP: 0018:ffffa5c206353ea8 EFLAGS: 00000246 ORIG_RAX: ffffffffffffffd9
>>>> [635607.740703] RAX: ffff8d72ffd20f00 RBX: 00024214f597c5b0 RCX: 000000000000001f
>>>> [635607.740703] RDX: 00024214f597c5b0 RSI: 0000000000020780 RDI: 0000000000000000
>>>> [635607.740704] RBP: 0000000000000004 R08: 002542bfbefa99fa R09: 00000000ffffffff
>>>> [635607.740705] R10: ffffa5c206353e88 R11: 00000000000000c5 R12: ffffffffaf0aaf78
>>>> [635607.740706] R13: ffff8d72ffd297d8 R14: 0000000000000000 R15: 00024214f58c2ed5
>>>> [635607.740709]  ? cpuidle_enter_state+0x91/0x2a0
>>>> [635607.740712]  do_idle+0x1d0/0x240
>>>> [635607.740715]  cpu_startup_entry+0x5f/0x70
>>>> [635607.740719]  start_secondary+0x185/0x1a0
>>>> [635607.740722]  secondary_startup_64+0xa5/0xb0
>>>> [635607.740731] p0xe0: hw csum failure
>>>> [635607.740745] CPU: 4 PID: 0 Comm: swapper/4 Not tainted 4.18.0-1 #1
>>>> [635607.740746] Hardware name: Supermicro Super Server/X10SRL-F, BIOS 2.0b 05/02/2017
>>>> [635607.740746] Call Trace:
>>>> [635607.740747]  <IRQ>
>>>> [635607.740750]  dump_stack+0x5c/0x7b
>>>> [635607.740755]  __skb_checksum_complete+0xb8/0xd0
>>>> [635607.740760]  __udp6_lib_rcv+0xa6b/0xa70
>>>> [635607.740767]  ? nft_do_chain_inet+0x7a/0xd0 [nf_tables]
>>>> [635607.740770]  ? nft_do_chain_inet+0x7a/0xd0 [nf_tables]
>>>> [635607.740774]  ip6_input_finish+0xc0/0x460
>>>> [635607.740776]  ip6_input+0x2b/0x90
>>>> [635607.740778]  ? ip6_rcv_finish+0x110/0x110
>>>> [635607.740780]  ipv6_rcv+0x2cd/0x4b0
>>>> [635607.740783]  ? udp6_lib_lookup_skb+0x59/0x80
>>>> [635607.740785]  __netif_receive_skb_core+0x455/0xb30
>>>> [635607.740788]  ? ipv6_gro_receive+0x1a8/0x390
>>>> [635607.740790]  ? netif_receive_skb_internal+0x24/0xb0
>>>> [635607.740792]  netif_receive_skb_internal+0x24/0xb0
>>>> [635607.740793]  napi_gro_frags+0x165/0x210
>>>> [635607.740796]  mlx4_en_process_rx_cq+0xa01/0xb40 [mlx4_en]
>>>> [635607.740802]  ? mlx4_cq_completion+0x23/0x70 [mlx4_core]
>>>> [635607.740807]  ? mlx4_eq_int+0x373/0xc80 [mlx4_core]
>>>> [635607.740810]  mlx4_en_poll_rx_cq+0x55/0xf0 [mlx4_en]
>>>> [635607.740811]  net_rx_action+0xe0/0x2e0
>>>> [635607.740813]  __do_softirq+0xd8/0x2e5
>>>> [635607.740816]  irq_exit+0xb4/0xc0
>>>> [635607.740817]  do_IRQ+0x85/0xd0
>>>> [635607.740820]  common_interrupt+0xf/0xf
>>>> [635607.740821]  </IRQ>
>>>> [635607.740823] RIP: 0010:cpuidle_enter_state+0xb4/0x2a0
>>>> [635607.740823] Code: 31 ff e8 df a6 ba ff 45 84 f6 74 17 9c 58 0f 1f 44 00 00 f6 c4 02 0f 85 d8 01 00 00 31 ff e8 13 81 bf ff fb 66 0f 1f 44 00 00 <4c> 29 fb 48 ba cf f7 53 e3 a5 9b c4 20 48 89 d8 48 c1 fb 3f 48 f7
>>>> [635607.740848] RSP: 0018:ffffa5c206353ea8 EFLAGS: 00000246 ORIG_RAX: ffffffffffffffd9
>>>> [635607.740849] RAX: ffff8d72ffd20f00 RBX: 00024214f597c5b0 RCX: 000000000000001f
>>>> [635607.740850] RDX: 00024214f597c5b0 RSI: 0000000000020780 RDI: 0000000000000000
>>>> [635607.740851] RBP: 0000000000000004 R08: 002542bfbefa99fa R09: 00000000ffffffff
>>>> [635607.740852] R10: ffffa5c206353e88 R11: 00000000000000c5 R12: ffffffffaf0aaf78
>>>> [635607.740853] R13: ffff8d72ffd297d8 R14: 0000000000000000 R15: 00024214f58c2ed5
>>>> [635607.740855]  ? cpuidle_enter_state+0x91/0x2a0
>>>> [635607.740857]  do_idle+0x1d0/0x240
>>>> [635607.740859]  cpu_startup_entry+0x5f/0x70
>>>> [635607.740861]  start_secondary+0x185/0x1a0
>>>> [635607.740863]  secondary_startup_64+0xa5/0xb0
> 
> As a matter of fact Dimitris found the issue in the patch and is working on a fix involving csum_block_sub()
> 
> Problems comes from trimming an odd number of bytes.

More exactly, trimming bytes starting at an odd offset.

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